Tuning

Why the engine needs extra fuel on a throttle hit

When the throttle snaps open, manifold pressure jumps and a rush of air heads for the cylinders. Some of the fuel already sprayed into the port is still clinging to the port walls, and the fuel calculation is always a fraction behind the airflow. The result is a brief lean spot right when you ask for power. Transient throttle enrichment covers that gap with a short burst of extra fuel whenever the throttle moves quickly.

On Elite ECUs that burst is shaped by five pieces:

Before you touch any of it

Transient tuning is the last layer, not the first. We only start it once three things are done:

1. The steady-state fuel map is right. If the base map is lean or rich at the cells you're moving through, you'll end up using transient enrichment to hide a fueling error, and it will never feel consistent.
2. Injection timing is sorted. Tune your injection angles for the best response with transient enrichment effectively out of the picture.
3. The engine is fully warm. Otherwise the coolant correction is mixing into everything you do.

Then set up a clean starting point: every setting and table at default, except Percentage Enrichment, which should be 100% in every cell. That way, while you tune sensitivity, you're always seeing the full amount.

Step 1: Enrichment Sensitivity

This table is tuned with the harshest throttle input you'll ever give the engine. With the engine idling, stab the throttle open as far and as fast as you can, then let it straight back off. There's no need to hold it open. Short stabs keep RPM down and keep stress off the engine.

While you do this, put the Transient Throttle Delta Load channel on a gauge. Write down the biggest value you see. You'll need it in step 3.

The table has RPM on one axis and the Transient Throttle Load Source, which is the throttle position you start the movement from, on the other. From idle you're starting at 0% throttle, so you're working in the 0% column near your idle RPM row. The default table's lowest row is 1000 RPM. Adjust those cells until the engine picks up crisply with no hesitation and no rich stumble.

Then work outward, one row and one starting position at a time. Some cells are hard or impossible to reach. For example, you probably can't sit at 1000 RPM with 10% throttle already open. Leave those cells following the shape of the ones around them.

Step 2: Percentage Async

Asynchronous enrichment is fired straight away, outside the normal injection schedule. Synchronous enrichment is added to the regular injector pulses. For the difference in more detail, see asynchronous vs synchronous enrichment.

At low RPM there's a long gap between injection events, so a large async share helps the engine respond immediately. As RPM rises the gap shrinks and a big async shot can be more than the engine needs in one go, so you reduce it to spread the fuel over the normal events. In practice you'll mostly be adjusting the bottom half of the RPM range. Above that, the table usually just carries on from where you left it.

Step 3: Percentage Enrichment

Sensitivity is tuned for the biggest, fastest hit. Most throttle movements on the street are much smaller and gentler, and they need only part of that fuel. This table sets that fraction.

1. Set the far-right Delta Load axis value to the largest Delta Load you recorded in step 1.
2. Check the cell under it is still 100%.
3. Now vary how fast and how far you move the throttle, so Delta Load lands at smaller values. With the table still at 100%, these part-throttle movements will be too rich.
4. Pull each cell down until those smaller movements feel as clean as the big one.

A worked example: say your biggest stab produced a Delta Load of 30%. Put 30 on the right-hand end of the axis at 100%. You might then find a gentle roll-on that gives 12% Delta Load only wants about three quarters of the full enrichment, so that cell ends up around 75%. Your numbers will differ. The point is that the table falls away as Delta Load drops.

Step 4: Enrichment Decay Rate

This sets how long the extra fuel hangs around after the throttle stops moving. The logic is easy to get backward, so remember:

• Enrichment lasts too long (rich after the pickup, lazy, smoky): raise the decay rate.
• Enrichment ends too soon (clean hit, then a lean stumble): lower the decay rate.

This one is hard to judge by feel. A fast wideband makes it much easier, because you can see whether lambda goes lean or stays rich in the second after the throttle stops moving.

Step 5: Coolant Temp Correction

A cold engine needs more transient fuel because less of it evaporates on cold port walls. You can only tune this during warm-up, and a cold engine warms fast, so have the laptop connected, the table open and your plan ready before you start it. Then check throttle response as coolant temperature climbs, adding or removing correction at each temperature as you pass through it. It usually takes a few cold starts to fill the table properly.

Troubleshooting

If you still have a flat spot after this, Transient Throttle Enhance is worth a look. And if you'd rather have it done on the dyno, book a free consultation with us.